This proposed research addresses fundamental questions about the effects of parenting on the development and behavior of adolescents with fragile X syndrome (FXS). It examines the transition to this life stage and investigates variables that may have a significant and continuing influence on adolescent behavior. As such, it takes a natural history approach to the study of FXS during this critical stage. We investigate the continuing impact of early parenting as well as parenting during adolescence on the development and behavior of 55 mother-child dyads that we have studied since early childhood. Our research to date has revealed the significant role that maternal responsivity, a key element of parent-child interaction, plays in the development of children with FXS. Our findings have underscored the fact that FXS is not just the product of innate biology, but is attributable to the dynamic and cumulative interaction of biology, behavior, and environment over time. Moreover, because it is a single gene disorder, FXS represents a rare opportunity to study the forces that shape adolescent development through the use of a number of fundamentally important child and parent variables. These variables include language, cognition, adaptive, social and problem behavior, autism symptoms, gender, and parenting provided by carrier mothers with the FXS premutation. This project will be led by Drs. Steven F. Warren and Nancy Brady at the University of Kansas Institute for Life Span Studies in collaboration with Dr. Elizabeth Berry-Kravis at Rush University Medical Center in Chicago, Dr. Leann Smith at the University of Wisconsin Waisman Center, and Dr. Kandace Fleming of KU. Building on 10 years of prior work with a fully intact longitudinal sample of 55 biological mothers and their full mutation children who are now adolescents, we propose to explore the impact of key behavioral variables on development and behavior through four aims. The first aim is to examine trajectories across all domains of child and mother behavior from early childhood through adolescence, and the relationship of gender, autism status, and child molecular measures to these trajectories. The second aim is to determine the effects of parenting before and during adolescence on a set of key adolescent outcomes. The third aim is to examine the effects of child (i.e., severity of behavior problems and pubertal status) and maternal (i.e., IQ, depression, maternal FXS premutation size and activation ratio, executive functioning, and family income) variables on parenting and mother-child relationship quality in adolescence. The fourth aim is to examine sequential relationships between specific adolescent behaviors and maternal behaviors during interactions. Reliable scientific knowledge of the dynamic interplay of children with FXS and their parenting experiences before and during the critical period of adolescence has important implications for the scientific understanding and clinical treatment of individuals with FXS and related conditions.